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Fix VMware layer tag reading #429

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merged 2 commits into from
Jan 21, 2021
Merged

Fix VMware layer tag reading #429

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e44094f
Fix VMware layer tag reading
cstation Jan 19, 2021
9ef3419
Improve VMware Tag reading
cstation Jan 21, 2021
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15 changes: 11 additions & 4 deletions volatility/framework/layers/vmware.py
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Original file line number Diff line number Diff line change
Expand Up @@ -48,8 +48,7 @@ def _read_header(self) -> None:
if magic not in [b"\xD2\xBE\xD2\xBE"]:
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raise VmwareFormatException(self.name, "Wrong magic bytes for Vmware layer: {}".format(repr(magic)))

# TODO: Change certain structure sizes based on the version
# version = magic[1] & 0xf
version = magic[0] & 0xf

group_size = struct.calcsize(self.group_structure)

Expand Down Expand Up @@ -81,12 +80,20 @@ def _read_header(self) -> None:
self._context.object("vmware!unsigned int",
offset = offset + name_len + 2 + (index * index_len),
layer_name = self._meta_layer))
data = self._context.object("vmware!unsigned int",
data_len = flags & 0x3f

# TODO: Read special data sizes (signalling a longer data stream) properly instead of skipping them
if data_len in (62, 63):
data_len = 4 if version == 0 else 8
offset += 2 + name_len + (indicies_len * index_len) + 2 * data_len
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So this confuses me, since it looks like we'd be doing this twice? Can you walk me through what's going on here please?

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@cstation cstation Jan 21, 2021 •
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I tried to clearify this a bit more in the next commit. Most tags have a data_len of 4 or 8, which are the regular cases and easy to handle. The layout looks as follows:

flags name_len name indices data
1 1 name_len 4 * indices_len data_len

Some tags however, have a data_len of 62 or 63, which indicate a longer datastream. The layout is than as follows:

flags name_len name indices data_size data_mem_size padding? data
1 1 name_len 4 * indices_len 4 or 8 4 or 8 2 data_size

The 4 or 8 (which I set as data_len) is version dependent, so this is where the version comes in. Difference between data_size and data_mem_size should occur in cases where the data is compressed (data_size < data_mem_size).

I based this mostly on Volatility 2.x-code and the original parser of the same author.

continue

data = self._context.object("vmware!unsigned int" if data_len == 4 else "vmware!unsigned long long",
layer_name = self._meta_layer,
offset = offset + 2 + name_len + (indicies_len * index_len))
tags[(name, tuple(indicies))] = (flags, data)
offset += 2 + name_len + (indicies_len *
index_len) + self._context.symbol_space.get_type("vmware!unsigned int").size
index_len) + data_len

if tags[("regionsCount", ())][1] == 0:
raise VmwareFormatException(self.name, "VMware VMEM is not split into regions")
Expand Down